Refrigerating apparatus



Dec. 19, 1961 Filed Aug. 31, 1959 E. C. SIMMONS EI'AL REFRIGERATINGAPPARATUS 2 Sheets-Sheet '1 I2 46 w n INVENTORS Edward 0. Simmons BY RoyR. Smith The/r Attorney Dec. 19, 1961 E. c. SIMMONS EI'AL 3,013,399

REFRIGERATING APPARATUS Filed Aug. 31, 1959 2 Sheets-Sheet 2 INVENTORS F2 Edward C. .Slmmons BY Roy R. Smith United States Patent 3,013,39?REFRIGERAIING APPARATU Edward C. Simmons and Roy R. Smith, Dayton, Ohio,assignors to General Motors (Jorporation, Detroit, Mich., a corporationof Deiawar'e Filed Aug. 31, 1959, Ser. No. 836,999 3 tJlaims. (Cl.62-151) This invention relates to refrigerating apparatus and moreparticularly to an improved arrangement for controlling the defrostingof the evaporator.

It is a well known fact that the. rate at which frost forms on theevaporator of a refrigerator varies from day to day depending upon theambient wet and dry bulb temperatures, the type of products placed in arefrigerator, the number and length of door openings, and similarfactors. Consequently, conventional defrost control systems operated bya clock or by the number of door openings do not cause defrosting totake place in accordance with actual defrost requirements.

It is an object of this invention to provide an improved defrost controlarrangement which automatically compensates for variations in many ofthe factors which vary the frequency at which defrosting should takeplace.

Another object'of this invention is to provide a defrost controlarrangement having improved reliability.

Still another object of this invention is to provide an automatic timingdevice which eliminates the need for use of mechanical timers such asclocks and the like which tend to become noisy and which are otherwiseunreliable or unsatisfactory.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein preferred embodiments of the present invention areclearly shown.

In the drawings:

FIGURE 1 is a schematic view showing a preferred embodiment of theinvention; and

FIGURE 2 is a schematic view showing a modified embodiment of theinvention.

Referring now to FIGURE 1 of the drawings wherein a preferred embodimentof the invention has been shown, reference numeral designates aconventional insulated freezer cabinet having a freezer compartment 12and a compressor compartment 14 provided therein. The compartment 12 isprovided with the usual type of access door 16 and is adapted to becooled by means of a con; ventional evaporator 18. The evaporator 18 isconnected in series refrigerant fiow relationship with a conventionalmotor compressor unit 20, a condenser unit 22 and a pressure reducingdevice 24. A thermostat 25, which is arranged to respond torefrigeration requirements in the compartment 12, serves to cycle thecompressor 20 so as to maintain the desired freezer compartmenttemperature.

During normal operation of the refrigerating system, frost willaccumulate on the evaporator 18 and as the result thereof, it becomesnecessary to remove period] cally this frost. For purposes ofillustration, there is shown an arrangement in which this is done bymeans of on electric heater 26 arranged in thermal exchange relationshipwith the evaporator 18. For purposes of illustrating the invention, theevaporator 18 has been shown disposed directly within the food storagecompartment 12, Whereas it could be located in any other suitablelocation, such as in a duct communicating with the food storagecompartment. Likewise, the heating coil 26 has been shown arrangedadjacent the lower edge of the evapora or 18 whereas this coil could bearranged so as to be in contact with a major portion of the evaporator18 or in thermal exchange relationship with a liquid reservoir formed asa part of the evaporator in accordance with well known defrostprinciples.

The control for the defrost heater 26 includes a hermetically sealedreceptacle 28 which may be made of glass or any other suitable material.The receptacle 23 is provided with an upper portion 30 which is arrangedin thermal exchange relationship with the contents of the frozen foodstorage compartment 12 and a lower portion 32 which is arranged inthermal exchange relationship with the machinery compartment wherein thecompressor and/or condenser 22 are located. A body of Water or similarliquid 34 is provided in the receptacle 28.

During normal operation of the refrigerator, the upper end of thereceptacle 28 will be subjected to below freezing temperatures and thelower end thereof will be subjected to temperatures considerably abovethe freezing temperature of water with the result that water disposedwithin the receptacle will tend to be vaporized by the heat surroundingthe lower end of the receptacle and most of the resulting Water vaporwill accumulate as frost on the inner wall surfaces of the upper end ofthe receptacle 28. The size of the receptacle and the quantity of waterdisposed therein are preferably designed so as to require approximatelytwenty-four hours for the evaporation of the water to take place underaverage temperature and refrigerator usage.

Power is supplied to the defrost heater 26 from the main power source36. Thus, a first conductor 38 connects the one side of the heater 26 tothe one side of the power source and a second conductor 40 serves toconnect the other side of the heater to the other side of the power linethrough a pair of thermostatic switches 42 and 45. The thermostaticswitch 42 is a conventional defrost limiter switch which serves to openthe circuit v to the defrost heater when the temperature of theevaporator indicates that all of the frost, which previously accumulatedon the evaporator,'has been melted.

An electric heater 44 which is connected to the power source 36 at alltimes serves to apply auxiliary heat to the lower end of the receptacle2% so as to facilitate evaporation of the Water therein. So long as anyappreciable amount of water remains in the lower end of the receptacle28, the heat 44 is incapable of providing enough heat to cause thethermostat 45 to close the circuit at 46 to initiate operation of thedefrost heater 26 but once the water in the receptacle 28 has beenvaporized andm-igrated to the upper end of the tube in the form offrost, the lower end of the tube and the thermostat 45 will ratherquickly become heated to a temperature high enough to initiate operationof the defrost heater 26. It will be noted that the bimetallicthermostat 45 includes a double set of contact-s so that when the upperend of the thermostat moves from the left to the right, as viewed inFIGURE 1 of the drawings, it opens the circuit to the motorcompressorvunit at 48 and closes the circuit to the defrost heater 26..During approximately twenty-four hours of the day under averagetemperature and refrigeration usage conditions, the thermostat 45 willmaintain the circuit at 4 8 closed'so as to provide for operation of thecompressor 20 at all times when the thermostat ,45 calls forrefrigeration. Once the thermostat 45 opens the circuit to the motorcompressor unit 20 and closes the circuit to the defrost heater 26, theaccumulated frost on the evaporator 18 will melt and this will occasionan increase in the temperature within the compartment 12 with the resultthat the frost accumulated in the upper end of the receptacle 28 willalso melt and will begin to refill the lower end of the receptacle 28.The direct of the frost melting in the receptacle 28 is to cause thelower end of the receptacle 28 to cool off. A small heater 27 isprovided for supply- 3 ing heat to the thermostat 45 during the defrostperiod to prevent premature restarting of the compressor prior tocomplete defrosting of the evaporator 18. The upper end of thereceptacle 28 is larger than the lower end thereof so as to prevent thefrost from sliding down the sides of the receptacle when it first beginsto melt.

Referring now to FIGURE 2 of the drawing wherein a modified type ofcontrol arrangement has been shown, the same reference numerals havebeen used to designate parts which are identical or similar inconstruction and function to the correspondingly numbered parts shown inFIGURE 1. The construction shown in FIGURE 2 of the drawings differsfrom the construction shown in F IGURE 1 primarily in that the sealedreceptacle 28 serves to house a float 50 which controls a switch 52disposed within the receptacle 28. The movable contactor of the switch52 is at all times electrically connected to a conductor 54 carried bythe float. The lower end of the conductor 54 extends into a body ofmercury 56 provided in the lower end of the receptacle 28. A lead wire58 which is connected to the source of power 36 extends through the wallof the receptacle 28 into the body of mercury 56, as shown. A quantityof water 34 is provided in the receptacle 2S and is adapted periodicallyto be at least partially vaporized so as to cause the float 50 to closethe switch 52 at spaced intervals of time depending on the length oftime for the water 34 to vaporize and migrate to the cold surfacesadjacent the upper end of the receptacle 28.

Closing of the switch 52 causes energization of a solenoid coil 68which, when energized, serves to raise the double pole, double throw,switch arm or bar 62. This upward movement of the switch bar 62 servesto break the circuit to the compressor motor 20 and make a circuit tothe defrost heater 26. An auxiliary contact bar 64 which is alsoactuated by the solenoid 60 serves to close a holding circuit 66 wherebythe solenoid 60 will remain energized irrespective of the position ofthe float operated switch 52 until the defrost limiter switch 42 opensthe circuit to the solenoid 60. The defrost limiter switch 42 willremain closed until the temperature of the evaporator 18 exceeds 36 F.at which time it will open the circuit including the solenoid 60 and thedefrost heater 26. Upon deenergization of the solenoid 60, the motorcontrol switch 62 will close the circuit leading to the compressor motorwith the result that the compressor motor will operate whenever thethermostatic switch 7 6 calls for refrigeration. The switch 70 ispreferably located in the food compartment so as to cause operation ofthe compressor whenever refrigeration is required. The type and locationof the freezer compartment temperature regulating switch 70 is broadlyimmaterial as any conventional refrigerant cycling control can be used.

The arrangement of the heater 36 in each of the circuits is preferablysuch that it will supply heat directly to the evaporator 18 and willalso assist in heating the upper end of the receptacle 28 by radiation,convection and if necessary by direct conduction. The size and locationof the heater 26 will, of course, vary with different size freezercompartments. It is also within the purview of this invention to place aportion of the heater 26 or an auxiliary heater directly on the upperend of the receptacle 23 when the construction and relative location ofthe parts is such that the main defrost heater 26 is incapable ofmelting the frost in the upper end of the receptacle 23 in the desiredtime.

While the embodiments of the present invention as herein disclosed,constitute preferred forms, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. In combination, a refrigerator cabinet having a food storagecompartment therein, an evaporator for cooling said food storagecompartment, refrigerant liquefying means supplying liquid refrigerantto said evaporator, means for defrosting said evaporator, control meansfor said defrosting means comprising a fluid receptacle having oneportion arranged in thermal exchange relationship with said food storagecompartment so as to condense and freeze moisture on the inner wallsthereof and having another portion arranged in thermal exchangerelationship with said refrigerant liquefying means so as to be heatedthereby, and means responsive to a predetermined change in fluid levelwithin said receptacle for initiating operation of said means fordefrosting said evaporator.

2. In combination, means forming an insulated food storage compartment,an evaporator in thermal exchange relationship to air for saidcompartment, a refrigerant liquefying means supplying liquid refrigerantto said evaporator, means for defrosting said evaporator, and controlmeans for said defrosting means comprising a receptacle having its upperportion arranged in thermal exchange relationship with said food storagecompartment, a quantity of liquid in said receptacle, means for applyingheat to said liquid so as to vaporize at least a portion thereof, andcans responsive to the vaporization of a predetermined quantity of saidliquid for initiating defrosting of said evaporator.

3. In combination, means forming an insulated food storage compartment,an evaporator arranged to cool the contents of said compartment, arefrigerant liquefying means for supplying liquid refrigerant to saidevaporator, means for defrosting said evaporator, control means for saiddefrosting means comprising a fluid receptacle having a first portionarranged in thermal exchange relationship with said food storagecompartment and having a second portion arranged in thermal exchangerelationship with a relatively warm zone whereby fluid therein vaporizesand migrates to said first portion, and means responsive to a givenchange in the liquid level in said second portion for controlling saidmeans for defrosting said evaporator.

References Cited in the file of this patent UNITED STATES PATENTS2,155,262 Fiene Apr. 18, 1939 2,303,182 Tobey Nov. 24, 1942 2,324,647Ray July 20, 1943 2,524,813 Lathrop Oct. 10, 1950 2,570,451 HottenrothOct. 9, 1951 2,735,272 Lange Feb. 21, 1956

